A conventional bicycle seat tube assembly generally includes a seat post which has a clamp unit for securing the seat on the top thereof and the seat post is inserted into the seat tube of the bicycle frame. Some of the seat tube assemblies can adjust the height of the seat and the tilt angle of the seat so as to meet different requirement for different users.
The conventional height adjustable seat tube assembly includes an inner tube which is movable linearly relative to an outer tube so as to adjust the height of the seat which is connected to the top of the inner tube. The conventional height adjustable devices comprise mechanical adjustable device, hydraulic adjustable device and hybrid adjustable device. The mechanical adjustable device uses mechanical way to move the inner tube relative to the outer tube. The hydraulic adjustable device uses hydraulic force to move the inner tube relative to the outer tube. The hybrid adjustable device uses both of the hydraulic force and pneumatic force to move the inner tube relative to the outer tube.
For the hydraulic height adjustable device and the hybrid height adjustable device, each of which generally includes a clamp unit, a seat post, an outer cylinder, an inner cylinder, a valve unit and a driving device. The valve unit is usually fixed to the lower end of the seat post or the outer cylinder. The valve unit regulates the volume of the hydraulic liquid in the two oil rooms. The position of the valve unit relates the space and the related positions between the parts.
Because the inner tube is linearly movable in the outer tube, and both of the inner and outer tubes are circular tubes, so that the inner tube may be rotatable relative to the outer tube. Therefore, a restriction unit for prevention of rotation of the inner tube relative the outer tube is developed and installed between the inner and outer tubes. By the restriction unit, the force that moves the inner tube relative to the outer tube is not used on the rotation of the inner tube relative to the outer tube.
Taiwan Utility Model 099117817 discloses a first tube having a first end and a second end, a second tube having a first end and a second end, wherein the first end of the second tube is opened so that the second end of the first tube is inserted into the first end of the second tube. A piston located in the hole of the first tube and forms an air room between the piston and the first end of the first tube. A valve unit is stationary relative to the second tube and defines a first oil room and a second oil room in the first tube. The first oil room is located between the valve unit and the piston, and the second oil room is located between the valve unit and the second end of the firs tube. The valve unit has a first check valve and a second check valve, wherein the first check valve stops the oil flow from the first oil room to the second oil room, and allows the oil flow from the second oil room to the first oil room. The second check valve stops the oil flow from the second oil room to the first oil room, and allows the oil flow from the first oil room to the second oil room. A movable control member is movable between the first and second check valves. When the movable control member is located at the first position, the oil passes through the first check valve and flows from the second oil room to the first oil room. When the movable control member is located at the second position, the oil passes through the second check valve and flows from the first oil room to the second oil room.
Taiwan Utility Model 099220386 discloses a first piston unit comprising a first cylinder, a first piston and an end cap. The first cylinder is connected to the bicycle frame and the first piston has a hollow interior space, the first end of the first piston is inserted into the first cylinder. The end of the first piston has a through hole. The second end of the first piston is connected to the bicycle seat. A gap is defined between the first piston and the first cylinder, the gap communicates with the interior of the first piston. The end cap is located at the opening of the first cylinder so as to seal the gap. A second piston unit comprises a second cylinder and a second piston. The second cylinder is located in the first piston and communicates with the interior of the first piston. The area of the cross section of the first cylinder is the same as the area of the cross section of the gap. The first end of the second piston extends through the through hole of the first piston and inserted into the second cylinder so that the gap, the interior of the first piston and the second cylinder form a first closed space. The second end of the second piston is connected to the inside of the first cylinder. The second piston has a hollow interior and communicates with the first cylinder so that the interior of the first cylinder and the interior of the second piston form a second closed space. A control valve is connected between the first piston and the second cylinder so as to control the communication between the first piston and the second cylinder. The first closed spaces stores oil and the second closed space stores air.
Both of the two examples mentioned above have a valve unit located at the underside of the outer cylinder and a restriction unit for prevention of rotation. The first embodiment shows the longitudinal slot in the inner tube and a key is engaged with the slot so as to prevent the inner tube from rotating relative to the outer tube. The restriction unit of the second embodiment has two flat surfaces located in the through hole and the outside of the piston, the two flat surfaces are matched with each other so as to prevent the two parts from rotating relative to each other.
However, the restriction unit cannot prevent the inner tube from dropping out from the outer tube and the leakage of the hydraulic oil. When the seat is adjusted, the inner tube is easily pulled out from the outer tube.
The present invention intends to provide a restriction unit for restricting the movement of the inner tube relative to the outer tube of bicycle seat tube assembly.